Rearrange some imports to ensure rattail.db.model comes last

this is necessary for Continuum versioning

tailbone/app.py

@@ -34,8 +34,7 @@ import sqlalchemy as sa
 import rattail.db
 from rattail.config import make_config
 from rattail.exceptions import ConfigurationError
-from rattail.db.util import get_engines
+from rattail.db.config import get_engines, configure_versioning
-from rattail.db.continuum import configure_versioning
 from rattail.db.types import GPCType
 
 import formalchemy as fa
@@ -44,8 +43,6 @@ from pyramid.authentication import SessionAuthenticationPolicy
 
 import tailbone.db
 from tailbone.auth import TailboneAuthorizationPolicy
-from tailbone.forms import renderers
-from tailbone.forms.alchemy import TemplateEngine
 
 
 def make_rattail_config(settings):
@@ -125,6 +122,9 @@ def make_pyramid_config(settings):
     """
     Make a Pyramid config object from the given settings.
     """
+    from tailbone.forms.alchemy import TemplateEngine
+    from tailbone.forms import renderers
+
     config = Configurator(settings=settings, root_factory=Root)
 
     # Configure user authentication / authorization.

tailbone/auth.py

@@ -28,8 +28,6 @@ from __future__ import unicode_literals, absolute_import
 
 import logging
 
-from rattail.db import model
-from rattail.db.auth import has_permission, authenticated_role
 from rattail.util import prettify, NOTSET
 
 from zope.interface import implementer
@@ -70,6 +68,8 @@ def session_timeout_for_user(user):
     """
     Returns the "max" session timeout for the user, according to roles
     """
+    from rattail.db.auth import authenticated_role
+
     roles = user.roles + [authenticated_role(Session())]
     timeouts = [role.session_timeout for role in roles
                 if role.session_timeout is not None]
@@ -88,6 +88,9 @@ def set_session_timeout(request, timeout):
 class TailboneAuthorizationPolicy(object):
 
     def permits(self, context, principals, permission):
+        from rattail.db import model
+        from rattail.db.auth import has_permission
+
         for userid in principals:
             if userid not in (Everyone, Authenticated):
                 if context.request.user and context.request.user.uuid == userid:

tailbone/forms/fields.py

@@ -28,8 +28,6 @@ from __future__ import unicode_literals, absolute_import
 
 import formalchemy as fa
 
-from rattail.db import model
-
 
 def AssociationProxyField(name, **kwargs):
     """
@@ -45,6 +43,7 @@ def AssociationProxyField(name, **kwargs):
                         self.renderer.deserialize())
 
     def value(model):
+        from rattail.db import model
         return getattr(model, name, None)
 
     kwargs.setdefault('value', value)